Aqueous vibration damping compositions

Abstract

The present invention provides an aqueous polymer dispersion for vibration damping comprising a film-forming polymer in the form of dispersed particles comprising a polymer phase P1 and different polymer phases P2 and P3; the polymer dispersion obtained by free radical emulsion polymerization. Controlling the difference in glass transition temperatures of the polymers in the various polymer phases results in effective sound damping as determined by a Damping Loss Factor of at least 0.1 over a temperature range of at least 40° C. determined at a frequency of 200 Hz over a temperature range of −10 to 65° C. Use of a chain transfer agent in the polymerization of the various monomer charges results in good appearance in the resultant vibration damping coating.

What is claimed is: 
     
       1. An aqueous polymer dispersion for vibration damping comprising a film-forming polymer in the form of dispersed particles comprising a polymer phase P1 and different polymer phases P2 and P3; the polymer dispersion obtained by free radical emulsion polymerization comprising the following steps:
 (a) polymerization of a first monomer charge M1 to give a polymer phase P1 followed by 
 (b) polymerization of a second monomer charge M2 in the presence of P1 to give a polymer phase P2, 
 (c) polymerization of a third monomer charge M3 in the presence of P1 and P2 to give a polymer phase P3, 
 
       wherein the difference in glass transition temperatures between P1 and P2 is at least 20° C.; the difference in glass transition temperatures between P2 and P3 is at least 5° C. and a chain transfer agent is used in the polymerization of the monomer charges M1, M2 and M3. 
     
     
       2. The aqueous polymer dispersion of  claim 1  wherein P1 has a glass transition temperature of −40 to 130° C. and P2 has a glass transition temperature of −40 to 130° C. and the difference in the glass transition temperatures between P1 and P2 is from 70 to 150° C. 
     
     
       3. The aqueous polymer dispersion of  claim 2  wherein P3 has a glass transition temperature of −10 to 70° C. and the difference in the glass transition temperatures between P2 and P3 is from 5 to 50° C. 
     
     
       4. The aqueous polymer dispersion of  claim 1  wherein the monomer charge M1 comprises from 5 to 25 percent by weight of at least one monomer M1a selected from C 1  to C 10  esters of acrylic acid; from 75 to 95 percent by weight of at least one monomer M1b selected from C 1  to C 4  alkyl esters of methacrylic acid; and from 0 to 5 percent by weight of one or more ethylenically unsaturated monomers different from and polymerizable with the monomers M1a and M1b. 
     
     
       5. The aqueous polymer dispersion of  claim 1  wherein the monomer charge M2 comprises from 60 to 90 percent by weight of at least one monomer M2a selected from C 1  to C 10  esters of acrylic acid; from 10 to 40 percent by weight of at least one monomer M2b selected from C 1  to C 4  alkyl esters of methacrylic acid; and from 0 to 5 percent by weight of one or more ethylenically unsaturated monomers different from and polymerizable with the monomers M2a and M2b. 
     
     
       6. The aqueous polymer dispersion of  claim 1  wherein the monomer charge M3 comprises from 30 to 50 percent by weight of at least one monomer M3a selected from C 1  to C 10  esters of acrylic acid; from 50 to 70 percent by weight of at least one monomer M3b selected from C 1  to C 4  alkyl esters of methacrylic acid; and from 0 to 5 percent by weight of one or more ethylenically unsaturated monomers different from and polymerizable with the monomers M3a and M3b. 
     
     
       7. The aqueous polymer dispersion of  claim 1  wherein M1 comprises from 30 to 50 percent by weight; M2 comprises from 30 to 50 percent by weight; and M3 comprises from 10 to 30 percent by weight; the percentages by weight being based on total weight of M1, M2 and M3. 
     
     
       8. The aqueous polymer dispersion of  claim 1  in which the chain transfer agent is a mercapto compound. 
     
     
       9. The aqueous polymer dispersion of  claim 1  in which the chain transfer agent is present in amounts of 0.1 to 3 percent by weight based on the weight of monomers contained in the respective monomer charge. 
     
     
       10. The aqueous polymer dispersion of  claim 1  that has a fourth polymer phase P4 which, after polymerization of the third monomer charge, a fourth monomer charge M4 is polymerized to give the polymer phase P4. 
     
     
       11. The aqueous polymer dispersion of  claim 10  wherein the polymerization of monomer charge M4 is conducted in the absence of a chain transfer agent. 
     
     
       12. The aqueous polymer dispersion of  claim 10  wherein the monomer charge M4 comprises from 30 to 50 percent by weight of at least one monomer M4a selected from C 1  to C 10  esters of acrylic acid; from 50 to 70 percent by weight of at least one monomer M4b selected from C 1  to C 4  alkyl esters of methacrylic acid; and from 0 to 2 percent by weight of one or more ethylenically unsaturated monomers different from and polymerizable with the monomers M4a and M4b. 
     
     
       13. The aqueous polymer dispersion of  claim 10  wherein M1 comprises from 30 to 50 percent by weight; M2 comprises from 30 to 60 percent by weight; M3 comprises from 10 to 30 percent by weight; and M4 comprises from 10 to 30 percent by weight; the percentages by weight being based on total weight of M1, M2, M3 and M4.